In fluid machinery, sliding portions are generally lubricated with oil in order to prevent seizing or abnormal wear or abrasion. Accordingly, a fluid discharged from the fluid machinery is somewhat mixed with the oil, and it is extremely difficult to remove the oil from the fluid. In view of this, use of bearings such as grease-filled ball bearings for the sliding portions has been suggested to perform lubrication only within the bearings for supply of a clean fluid (see, for example, Patent Document 1).
Patent Document 1: Japanese Laid-Open Utility Model Publication No. 62-59788 (pages 9 and 10, FIG. 1)
Use of grease-filled bearings is not limited, to fluid machinery, and they are generally used in various fields including the field of autommotive vehicles, the field of medical machinery and the like. Such grease-filled bearings have two sealing materials disposed on respective sides thereof that prevent grease from being mixed with dust or moisture in an atmosphere. If a grease-filled bearing merely supports a rotational motion, grease filled inside would never leak outside the bearing.
However, in a case of a scroll fluid machine in which an orbital scroll undergoes an orbiting motion relative to a stationary scroll to compress a fluid, the orbiting motion of the orbital scroll is performed with a certain fixed radius and, hence, a centrifugal force acts on bearings mounted on the orbital scroll. Because of this, such a phenomenon occurs that grease filled inside oozes out from an end surface of a sealing material and scatters outside.
Further, of a plurality of bearings located inside a compressor, some are subject to a pressure difference generated between opposite sides thereof, which sometimes promotes leakage of grease. If leakage of grease occurs, not only is reliability of these bearings reduced, but there is also a good chance that fluid discharged is mixed with the grease.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide an air supply device capable of prolonging life of bearings mounted therein, enhancing reliability of the bearings, and supplying clean air without causing any leakage of grease from the bearings.